The present invention relates to strip chart recorders and strip chart paper for use therein.
Strip chart recorders provide a means of producing a permanent record of data for numerous uses. For example, in physiological monitoring, it is frequently desirable to make a permanent record of data from a patient monitor for diagnostic purposes. When making a record of medical data, it is especially important that all data of interest be recorded without interruption. However, if the supply of strip chart recording paper in the recorder is exhausted unknown to the user, time is lost while a new supply of paper is installed in the recorder and important data can be lost.
A further hazard exists in the use of strip chart recorders which utilize thermal print heads to make a record on heat sensitive strip chart paper. Typically, the thermal print head is disposed to press the paper between the head and a moving printing platen, so that the paper is pressed closely against the print head by the platen as the platen advances the paper. The platen must have a high coefficient of friction to ensure that the paper will not slip. Consequently, if the paper between the print head and the platen runs out, the platen may damage the relatively fragile thermal print head through abrasion if the platen continues to move.
Some suppliers of strip chart paper provide a small mark near the end of each roll of paper so that the user may determine that the end of the paper is near if the user should happen to see the mark. However, such markings are intentionally made unobstrusive to avoid obscuring data and, therefore, are not often seen by the user before the paper runs out. The user also is often preoccupied with other matters. Accordingly, the low paper condition frequently is not noticed.